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Activation Energy (activation + energy)
Kinds of Activation Energy Terms modified by Activation Energy Selected AbstractsCarbon-Centered Radical Addition and ,-Scission Reactions: Modeling of Activation Energies and Pre-exponential FactorsCHEMPHYSCHEM, Issue 12 2009Maarten K. Sabbe No abstract is available for this article. [source] Ab Initio Group Contribution Method for Activation Energies of Hydrogen Abstraction ReactionsCHEMPHYSCHEM, Issue 1 2006Mark Saeys Prof. Abstract The group contribution method for activation energies is applied to hydrogen abstraction reactions. To this end an ab initio database was constructed, which consisted of activation energies calculated with the ab initio CBS-QB3 method for a limited set of well-chosen homologous reactions. CBS-QB3 is shown to predict reaction rate coefficients within a factor of 2,4 and Arrhenius activation energies within 3,5 kJ,mol,1of experimental data. Activation energies in the set of homologous reactions vary over 156 kJ,mol,1with the structure of the abstracting radical and over 94 kJ,mol,1with the structure of the abstracted hydrocarbon. The parameters required for the group contribution method, the so-called standard activation group additivity values, were determined from this database. To test the accuracy of the group contribution method, a large set of 88 additional activation energies were calculated from first principles and compared with the predictions from the group contribution method. It was found that the group contribution method yields accurate activation energies for hydrogen-transfer reactions between hydrogen molecules, alkylic hydrocarbons, and vinylic hydrocarbons, with the largest deviations being less than 6 kJ,mol,1. For reactions between allylic and propargylic hydrocarbons, the transition state is believed to be stabilized by resonance effects, thus requiring the introduction of an appropriate correction term to obtain a reliable prediction of the activation energy for this subclass of hydrogen abstraction reactions. [source] Variation of the Effective Activation Energy Throughout the Glass TransitionMACROMOLECULAR RAPID COMMUNICATIONS, Issue 19 2004Sergey Vyazovkin Abstract Summary: An advanced isoconversional method has been applied to determine the effective activation energies (E) for the glass transition in polystyrene (PS), poly(ethylene terephthalate) (PET), and boron oxide (B2O3). The values of E decrease from 280 to 120 kJ,·,mol,1 in PS, from 1,270 to 550 kJ mol,1 in PET, and from 290 to 200 kJ mol,1 in B2O3. It is suggested that a significant variation in E should be observed for the fragile glasses that typically include polymers. Variation in the effective activation energy of PS, PET, and B2O3 with temperature. [source] Thermal Decomposition of NTO: An Explanation of the High Activation EnergyPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 4 2007Valery Abstract Burning rate characteristics of the low-sensitivity explosive 5-nitro-1,2,4-triazol-3-one (NTO) have been investigated in the pressure interval of 0.1,40,MPa. The temperature distribution in the combustion wave of NTO has been measured at pressures of 0.4,2.1,MPa. Based on burning rate and thermocouple measurements, rate constants of NTO decomposition in the molten layer at 370,425,°C have been derived from a condensed-phase combustion model (k=8.08,1013,exp(,19420/T) s,1. NTO vapor pressure above the liquid (ln P=,9914.4/T+14.82) and solid phases (ln P=,12984.4/T+20.48) has been calculated. Decomposition rates of NTO at low temperatures have been defined more exactly and it has been shown that in the interval of 180,230,°C the decomposition of solid NTO is described by the following expression: k=2.9,1012,exp(,20680/T). Taking into account the vapor pressure data obtained, the decomposition of NTO in the gas phase at 240,250,°C has been studied. Decomposition rate constants in the gaseous phase have been found to be comparable with rate constants in the solid state. Therefore, a partial decomposition in the gas cannot substantially increase the total rate. High values of the activation energy for solid-state decomposition of NTO are not likely to be connected with a sub-melting effect, because decomposition occurs at temperatures well below the melting point. It has been suggested that the abnormally high activation energy in the interval of 230,270,°C is a consequence of peculiarities of the NTO transitional process rather than strong bonds in the molecule. In this area, the NTO molecule undergoes isomerization into the aci -form, followed by C3-N2 heterocyclic bond rupture. Both processes depend on temperature, resulting in an abnormally high value of the observed activation energy. [source] Synthesis and Reactivity of Enediynyl Amino Acids and Peptides: A Novel Concept in Lowering the Activation Energy of Bergman Cyclization by H-Bonding and Electrostatic Interactions.CHEMINFORM, Issue 7 2004Amit Basak No abstract is available for this article. [source] Studies on multiphased mixed crystals of NaCl, KCl and KICRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2009M. Priya Abstract Multiphased mixed crystals of NaCl, KCl and KI were grown by the melt method, for the first time. Densities and refractive indices of all the grown crystals were determined and used for the estimation of the composition in the crystal. Atomic absorption spectroscopic measurements were done to estimate the metal atom contents in the crystal. Lattice parameters and thermal parameters (Debye-Waller factor, mean square amplitude of vibration, Debye temperature and Debye frequency) were determined from the X-ray powder diffraction data. DC and AC electrical measurements were done at various temperatures ranging from 40 to 150°C. Activation energies were also estimated. The observed lattice parameters showed that the system exhibits three phases each nearly corresponds to NaCl, KCl and KI. The thermal and electrical parameters show a highly nonlinear bulk composition dependence. Results are reported. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Swift hopping gallium over [AlO4], tetrahedra in Ga/ZSM-5: A DFT studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2007Ilya V. Kusmin Abstract Density functional theory calculations were carried out to investigate gallium species (Ga+, [GaH2]+, and [GaO]+) stabilization in Ga-exchanged HZSM-5, using cluster modeling approach. Three isomeric gallium positions over [AlO4], zeolite fragment at T12 position were found. These isomers are turning into each over with low activation energy barrier and gallium fragment revolves around [AlO4], tetrahedron by hopping between cationic positions. Activation energies of gallium fragment hopping were computed and compared for different gallium containing cations. Those barriers were found to be times less than the activation energies of catalytic processes on gallium-exchanged zeolite. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Color Stability of Edible Coatings During Prolonged StorageJOURNAL OF FOOD SCIENCE, Issue 7 2000T.A. Trezza ABSTRACT: The yellowing rates of edible coatings were determined at 23, 40, and 55 °C at 75% relative humidity (RH). Whey protein isolate (WPI) coatings had lower yellowing rates than whey protein concentrate (WPC) and the same rates as shellac coatings. Hydroxypropyl methylcellulose (HPMC) coatings had the lowest yellowing rates. Zein coatings became less yellow during storage; however, their color was still pronounced. Activation energies and Q10 values for the yellowing of whey protein coatings were similar to those previously reported for the browning of whey powder. The results indicate that WPI coatings can be used in place of shellac coatings when low-color development is desired. WPC coatings can be used to tailor color development of a food. [source] Novel tetracyclic imidazole derivatives: Synthesis, dynamic NMR study, and anti-inflammatory evaluationJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 3 2010Renata Rup A series of tetracyclic imidazole derivatives 9a,9v and 10a,10h are prepared by multistep route starting from the known tricyclic diketones 2a,2d. Intermediary dibenzooxepin[4,5- d]imidazoles (3a, 3c) and dibenzothiepin[4,5- d]imidazoles (3b, 3d) are N -protected to 4e, 4f and to the isomeric compounds 5a, 5b and 6a, 6b. The isomeric compounds 5 and 6 are separated. Compounds 4, 5, and 6 are formylated at C(2) to afford 7a,7j. In the last steps, aldehyde group is reduced, then alkylated to the two sets of isomeric ,-dimethylaminoalkyl derivatives 9a,9v. N -deprotection of 9i,9v led to the compounds 10a,10h. Assignment of the syn/anti structure to 5a and 6a was supported by 1D selective ROESY NMR spectra, whereas conformational mobility for the selected representatives 8a and 8b is studied by dynamic NMR. Activation energies (energy barriers for interconversion) are determined to be ,11.5 and 16.2 kcal/mol, respectively. A series of derivatives 9 and 10 were tested in vitro for their anti-inflammatory activity. J. Heterocyclic Chem., (2010). [source] The kinetics of the reduction of iron oxide by carbon monoxide mixed with carbon dioxideAICHE JOURNAL, Issue 4 2010C. D. Bohn Abstract Results are reported for the repeated reduction of iron oxide particles, 300,425 ,m diameter, by a mixture of CO, CO2, and N2 in a fluidized bed of 20 mm internal diameter. The conclusions were as follows: (1) Reduction of either Fe2O3 to Fe3O4 or of Fe3O4 to Fe0.947O is first-order in CO. (2) With the particle sizes used, the rates of the reduction reactions are controlled by intrinsic chemical kinetics. Activation energies and pre-exponential factors are reported. (3) The first cycle gave anomalous results, but (a) the rate of reduction of Fe2O3 to Fe3O4 remained constant over cycles 2,10; (b) the rate of reduction of Fe3O4 to Fe0.947O declined by 60,85% over cycles 2,10. (4) The rates of reduction declined with solids conversion down to zero at 80% conversion. The rates were incorporated into a conventional model of a fixed bed, which was used to predict, satisfactorily, the reduction behavior of iron oxide. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] The kinetics of enhanced spin capturing polymerization: Influence of the nitrone structureJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2009Edgar H. H. Wong Abstract Several nitrones and one nitroso compound have been evaluated for their ability to control the molecular weight of polystyrene via the recently introduced radical polymerization method of enhanced spin capturing polymerization (ESCP). In this technique, molecular weight control is achieved (at ambient or slightly elevated temperatures) via the reaction of a growing radical chain with a nitrone forming a macronitroxide. These nitroxides subsequently react rapidly and irreversibly with propagating macroradicals forming polymer of a certain chain length, which depends on the nitrone concentration in the system. Via evaluation of the resulting number-average molecular weight, Mn, at low conversions, the addition rate coefficient of the growing radicals onto the different nitrones is determined and activation energies are obtained. For the nitrones N - tert -butyl-,-phenylnitrone (PBN), N -methyl-,-phenylnitrone (PMN), and N -methyl-,-(4-bromo-phenyl) nitrone (pB-PMN), addition rate coefficients, kad,macro, in a similar magnitude to the styrene propagation rate coefficient, kp, are found with spin capturing constants CSC (with CSC = kad,macro/kp) ranging from 1 to 13 depending on the nitrone and on temperature. Activation energies between 23.6 and 27.7 kJ mol,1 were deduced for kad,macro, congruent with a decreasing CSC with increasing temperature. Almost constant Mn over up to high monomer to polymer conversions is found when CSC is close to unity, while increasing molecular weights can be observed when the CSC is large. From temperatures of 100 °C onward, reversible cleavage of the alkoxyamine group can occur, superimposing a reversible activation/deactivation mechanism onto the ESCP system. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1098,1107, 2009 [source] Phase behaviour of microemulsions with lubricant base oil as the oil phaseLUBRICATION SCIENCE, Issue 7 2009Ya Lu Abstract Appropriate surfactants and co-surfactants were chosen to prepare a microemulsion system with lubricant base oil as the oil phase. The phase behaviour of the microemulsion at different temperatures and at different oil/water mass ratios was assessed on the basis of conductivity measurements. Microemulsions and a bi-continuous microstructure were obtained when the oil/water mass ratio was below 0.33. An analysis of the conductivity behaviour of the microemulsions revealed that different conductive mechanisms are operative at different water contents. Activation energies (,E) were determined. The results showed that ,E increases with increasing water content. The data and the derived relationship provided a basis for preparing metalworking microemulsions. Copyright © 2009 John Wiley & Sons, Ltd. [source] A Kinetic Study on the Thermal Degradation of Multi-Walled Carbon Nanotubes-Reinforced Poly(propylene) CompositesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2004Min-Kang Seo Abstract Summary: The influence of the multi-walled carbon nanotubes (MWNTs) content on the thermal degradation behavior of MWNTs-reinforced poly(propylene) (PP) composites was investigated by using non-isothermal thermogravimetric analysis (TGA). Kinetic parameters of degradation were evaluated by using the Flynn-Wall-Ozawa iso-conversional method and the pseudo first-order method. As a result, compared with pristine PP, MWNTs-PP nanocomposites have lower peak temperatures of degradation, narrower degradation temperature ranges and a higher amount of residual weight at the end of the degradation, which is likely to be a result of specific interactions between complimentary functional groups. The values of the reaction order of MWNTs-PP nanocomposites determined by the Kissinger method are close to 1 in the non-isothermal degradation process. There is a good correlation between the Ea in region II and the peak temperature of degradation for the composites. Activation energies for degradation of different contents of MWNTs-filled PP nanocomposites as a function of conversion. [source] The kinetics of competitive antagonism of nicotinic acetylcholine receptors at physiological temperatureTHE JOURNAL OF PHYSIOLOGY, Issue 4 2008Deeptankar Demazumder Detailed information about the ligand-binding site of nicotinic acetylcholine receptors has emerged from structural and mutagenesis experiments. However, these approaches provide only static images of ligand,receptor interactions. Kinetic measurements of changes in protein function are needed to develop a more dynamic picture. Previously, we measured association and dissociation rate constants for competitive inhibition of current through embryonic muscle acetylcholine receptor channels at 25°C. Little is known about competitive antagonism at physiological temperatures. Here, we performed measurements at 37°C and used thermodynamics to estimate the energetics of antagonism. We used rapid solution exchange protocols to determine equilibrium and kinetics of inhibition of acetylcholine-activated currents in outside-out patches by (+)-tubocurarine, pancuronium and cisatracurium. Kinetic rates as high as 600 s,1 were resolved by this technique. Binding was primarily enthalpy driven. The 12°C increase in temperature decreased equilibrium antagonist binding by 1.7- to 1.9-fold. In contrast, association and dissociation rate constants increased 1.9- to 6.0-fold. Activation energies for dissociation were 90 ± 6, 106 ± 8 and 116 ± 10 kJ mol,1 for cisatracurium, (+)-tubocurarine and pancuronium, respectively. The corresponding apparent activation energies for association were 38 ± 6, 85 ± 6 and 107 ± 13 kJ mol,1. The higher activation energy for association of (+)-tubocurarine and pancuronium compared with cisatracurium is notable. This may arise from either a more superficial binding site for the large antagonist cisatracurium compared to the other ligands, or from a change in receptor conformation upon binding of (+)-tubocurarine and pancuronium but not cisatracurium. Differences in ligand desolvation and ligand conformation are not likely to be important. [source] Combinatorial Initiated CVD for Polymeric Thin Films,CHEMICAL VAPOR DEPOSITION, Issue 11 2006P. Martin Abstract A new combinatorial initiated (i)CVD system is fabricated and used to efficiently determine the deposition kinetics for two new polymeric thin films, poly(diethylaminoethylacrylate) (PDEAEA) and poly(dimethylaminomethylstyrene) (PDMAMS). The results of combinatorial depositions are compared to blanket iCVD under identical conditions using the appropriate vinyl monomer with tert -amylperoxide as the initiator. Fourier transform infrared spectroscopy (FTIR) reveals similar chemical structure in blanket and combinatorial films. FTIR also shows that functional groups are retained in iCVD of PDMAMS, whereas essentially all fine chemical structure of the material is destroyed in plasma-enhanced (PE)CVD. The maximum observed growth rates of PDEAEA and PDMAMS were 43 and 11,nm,min,1, respectively. The activation energy of growth with respect to filament temperature (Ea,filament) was 88.4±1.6 kJ,mol,1 for PDEAEA and 42.0±1.7 kJ,mol,1 for PDMAMS. Activation energies for growth with respect to substrate temperature (Ea,substrate) are ,59.5±2.7 kJ,mol,1 for PDEADA and ,82.7±2.6 kJ,mol,1 for PDMAMS, with the negative values consistent with adsorption-limited kinetics. The molecular weight of PDEAEA films ranges from 1 to 182 kDa as a function of substrate temperature. It is found that in all cases the combinatorial system agreed (within experimental uncertainty) with results of blanket iCVD, thus validating the use of the combinatorial system for future iCVD studies. [source] Tin-Free Radical Alkoxyamine Addition and Isomerization Reactions by Using the Persistent Radical Effect: Variation of the Alkoxyamine StructureCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2005Kian Molawi Dipl.-Chem. Abstract Various C-centered radicals can efficiently be generated through thermal CO-bond homolysis of alkoxyamines. This method is used to perform environmentally benign radical cyclization and intermolecular addition reactions. These alkoxyamine isomerizations and intermolecular carboaminoxylations are mediated by the persistent radical effect (PRE). In the paper, the effect of the variation of the alkoxyamine structure,in particular steric effects in the nitroxide moiety,on the outcome of the PRE mediated radical reactions will be discussed. Fourteen different nitroxides were used in the studies. It will be shown that reaction times can be shortened about 100 times upon careful tuning of the alkoxyamine structure. Activation energies for the CO-bond homolysis of the various alkoxyamines are provided. The kinetic data are used to explain the reaction outcome of the PRE-mediated processes. [source] Ab Initio Group Contribution Method for Activation Energies of Hydrogen Abstraction ReactionsCHEMPHYSCHEM, Issue 1 2006Mark Saeys Prof. Abstract The group contribution method for activation energies is applied to hydrogen abstraction reactions. To this end an ab initio database was constructed, which consisted of activation energies calculated with the ab initio CBS-QB3 method for a limited set of well-chosen homologous reactions. CBS-QB3 is shown to predict reaction rate coefficients within a factor of 2,4 and Arrhenius activation energies within 3,5 kJ,mol,1of experimental data. Activation energies in the set of homologous reactions vary over 156 kJ,mol,1with the structure of the abstracting radical and over 94 kJ,mol,1with the structure of the abstracted hydrocarbon. The parameters required for the group contribution method, the so-called standard activation group additivity values, were determined from this database. To test the accuracy of the group contribution method, a large set of 88 additional activation energies were calculated from first principles and compared with the predictions from the group contribution method. It was found that the group contribution method yields accurate activation energies for hydrogen-transfer reactions between hydrogen molecules, alkylic hydrocarbons, and vinylic hydrocarbons, with the largest deviations being less than 6 kJ,mol,1. For reactions between allylic and propargylic hydrocarbons, the transition state is believed to be stabilized by resonance effects, thus requiring the introduction of an appropriate correction term to obtain a reliable prediction of the activation energy for this subclass of hydrogen abstraction reactions. [source] Molecular dynamics simulation of self-diffusion coefficient and its relation with temperature using simple Lennard-Jones potentialHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2008Li Wei-Zhong Abstract The diffusion coefficient is indispensable to chemical engineering design and research. In practical engineering and research, there is still a great lack of available data. Therefore, methods need to be developed to solve this problem. In this paper, a molecular dynamics simulation method is used to predict the self-diffusion coefficient for a simple fluid by using the Green, Kubo relation (VACF) and the Einstein relation (MSD). The simulation results are in good agreement with experimental findings except for an error of about 10%. The algorithm average of the two methods (AV) reduces the error to 7%. The relationship of the diffusion coefficient with temperature has also been simulated. According to the simulation data, whose correlation is all above 0.99, the diffusion coefficient agrees well with temperature following the Arrenhius relationship. Activation energy for self-diffusion has been calculated and the result were 1258(VACF), 1272(MSD), and 1265(AV) J/mol separately. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(2): 86,93, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20191 [source] Modelling of air drying of fresh and blanched sweet potato slicesINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 2 2010Kolawole O. Falade Summary Effects of blanching, drying temperatures (50,80 °C) and thickness (5, 10 and 15 mm) on drying characteristics of sweet potato slices were investigated. Lewis, Henderson and Pabis, Modified Page and Page models were tested with the drying patterns. Page and Modified Page models best described the drying curves. Moisture ratio vs. drying time profiles of the models showed high correlation coefficient (R2 = 0.9864,0.9967), and low root mean squared error (RMSE = 0.0018,0.0130) and chi-squared (,2 = 3.446 × 10,6,1.03 × 10,2). Drying of sweet potato was predominantly in the falling rate period. The temperature dependence of the diffusion coefficient (Deff) was described by Arrhenius relationship. Deff increased with increasing thickness and air temperature. Deff of fresh and blanched sweet potato slices varied between 6.36 × 10,11,1.78 × 10,9 and 1.25 × 10,10,9.75 × 10,9 m2 s,1, respectively. Activation energy for moisture diffusion of the slices ranged between 11.1 and 30.4 kJ mol,1. [source] Kinetics and thermodynamics of glucoamylase inhibition by lactate during fermentable sugar production from food wasteJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2010Xiao Qiang Wang Abstract BACKGROUND: Glucoamylase hydrolysis is a key step in the bioconversion of food waste with complicated composition. This work investigated the effect of lactate on glucoamylase from Aspergillus niger UV-60, and inhibition mechanisms of glucoamylase by lactate during food waste hydrolysis. RESULTS: For 125 min hydrolysis of food waste (10%, dry basis), reducing sugars produced in the absence of lactate were 15%, 26% and 56% more than those produced in the presence of 24 g L,1 lactate at 60, 50 and 40 °C, respectively. Kinetic study showed that the type of glucoamylase inhibition by lactate was competitive, and Km (Michaelis-Menten constent), Vmax (maximum initial velocity), KI (inhibition constant) were 103.2 g L,1, 5.0 g L,1 min,1, 100.6 g L,1, respectively, for food waste hydrolysis at 60 °C and pH 4.6. Lactate also accelerated glucoamylase denaturation significantly. Activation energy of denaturation without inhibitor was 61% greater than that of denaturation with inhibitor (24 g L,1 lactate). Half-lives (t1/2) without inhibitor were 7.6, 2.7, 2.6, 1.7 and 1.2 times longer than those with inhibitor at temperature 40, 45, 50, 55 and 60 °C, respectively. CONCLUSION: These results are helpful to process optimization of saccharification and bioconversion of food waste. Copyright © 2010 Society of Chemical Industry [source] THIN-LAYER DRYING KINETICS OF SESAME HULLS UNDER FORCED CONVECTION AND OPEN SUN DRYINGJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2007MAJDI A. AL-MAHASNEH ABSTRACT Sesame hulls are a useful by-product of the sesame processing industry. The sesame hulls are produced at a high moisture content (68% wet basis) and need further drying to prevent deterioration. In this study, both open sun drying (OSD) and forced convection drying (FCD) at 42, 55, and 76C and 1.2 m/s air velocity were investigated. Six common thin-layer drying models were fitted to the experimental data. Several statistical parameters were used to evaluate the performance of thin-layer drying models, including r2, x2, root mean square error (RMSE) and residuals. Sesame hull drying was found to take place completely in the falling rate region. The modified Page model was found to describe OSD data well, while the Wang and Singh model was the best model for describing FCD. Effective diffusivity was found to be 1.89 × 10 - 8 m2/s and 7.36 × 10 - 10 to 1.20 × 10 - 9 m2/s for OSD and FCD, respectively. Activation energy was also found to be 12.95 kJ/mol for FCD. [source] Kinetics of Lysine and Other Amino Acids Loss During Extrusion Cooking of Maize GritsJOURNAL OF FOOD SCIENCE, Issue 2 2003S. Ilo ABSTRACT: Maize grits were extrusion-cooked in a conical, counter-rotating twin-screw extruder at different barrel temperatures, feed moistures, and screw speeds. Residence time distribution was measured by a dye tracer technique. Experiments with lysine-fortified maize grits showed a 1st order reaction for lysine loss. A detailed kinetic study has been performed for the losses during extrusion cooking of lysine, cystine, and arginine. The 1st-order rate constants were dependent mainly on product temperature and feed moisture, whereas screw speed had no influence. Activation energy of lysine, arginine, and cystine loss was 127, 68, and 76 kJ/mol, respectively. Shear stress significantly affected the rate constants of amino acids loss in extrusion cooking. [source] Curing Behavior of Epoxy Resin Using Controllable Curing Agents Based on Nickel ComplexesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 2 2006Abdollah Omrani Abstract Summary: The curing reaction kinetics and mechanism of the diglycidyl ether of bisphenol A (DGEBA) with three complexes of Ni(II) with diethylentriamine (Dien), Pyrazole (Pz) and Pyridine (Py) as ligands have been studied using differential scanning calorimetry (DSC). The curing reaction was characterized by high cure onset and peak maximum temperatures. The kinetics of the curing reaction were evaluated using the Ozawa method. The average values of activation energy for the three nickel complexes increased in the order: Dien-based curing agent,>,Pz-based curing agent,>,Py-based curing agent. Three main curing mechanisms (catalytic, complex cation and free ligand polymerization path) have been proposed depending on the cure temperature. It was also shown that the cure kinetics of DGEBA with Dien- and Py-based complexes could be described by the Sestak-Berggren equation. The water absorption, chemical resistance and thermal stability of the thermosets were also studied. The results showed that the thermoset obtained with the Py-based complex was more thermally stable than those obtained with the other two curing agents. Activation energy versus conversion plots for the epoxy systems studied. [source] Activation energy of thermally grown silicon dioxide layers on silicon substratesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2009G. Gerlach Abstract A detailed numerical consideration is used as basic approach for calculating profiles of activation energy versus oxide thickness for various temperatures between 780 and 930,°C. Results presented here are intentionally not based on models of diffusion and reaction kinetics to avoid introducing correction terms due to the expansion of theory still under discussion. The statistical calculation gives the mean activation energy of 2.01,eV with standard deviation of 0.10,eV, very close to the overall activation energy of 2.05,eV [M. A. Rabie, Y. M. Haddara, and J. Carette, J. Appl. Phys. 98, 074904 (2005)]. More instructive features of the thermal oxidation of silicon have been disclosed directly from measurements of oxide thickness with time [M. A. Hopper, R. A. Clarke, and L. Young, J. Electrochem. Soc. 122, 1216 (1975) and J. Blanc, Philos. Mag. B 55, 685 (1987)]. Graphs of the natural logarithm of the growth rate versus oxide thickness, in the range between 2 and 65,nm, show that the oxide thickness influences the activation energy EA between 1.4 and 2.7,eV. [source] Activation energy of Mg in a -plane Ga1,xInx N (0 < x < 0.17)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2009Daisuke Iida Abstract We investigated the electrical properties of Mg-doped Ga1,xInx N grown on an a -plane template. High-hole-concentration p-type Mg-doped Ga1,xInx N films with an InN molar fraction of 0.17 were fabricated on sidewall-epitaxial-lateral overgrown a -plane GaN grown on an r -plane sapphire substrate by MOVPE. Variable-temperature Hall effect measurement showed that a maximum hole concentration of 1.4 × 1019 cm,3 for x = 0.17 was reproducibly achieved at room temperature. The activation energy of Mg acceptors in Mg-doped a -plane Ga0.83In0.17N was found to be as low as 48 meV. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermal, mechanical, and diffusional properties of nylon 6/ABS polymer blends: Compatibilizer effectPOLYMER ENGINEERING & SCIENCE, Issue 7 2000Seung Phil Jang The thermal, mechanical, and water absorption properties of blends of nylon 6 (PA6) and acrylonitrile-butadiene-styrene copolymer (ABS) with and without the compatibilizer maleic anhydride (MAH) were studied. Polymers were melt-blended using a twin screw extruder, and injection molded into sheets. Tensile and impact properties, hardness, heat deflection resistance, and dimensional stability were enhanced by the incorporation of MAH. Synergistic effects were observed for tensile elongation and flexural properties. The melting temperature and the thermal stability were not significantly affected by the incorporation of MAH. The mechanical property enhancement by the introduction of compatibilizer was explained by the formation of a micro-domain structure in the blends. The equilibrium water uptake increased with increasing concentration of PA6, and the diffusion coefficient was determined from the water transport kinetics at different temperatures. Activation energy was extracted from the temperature dependence of the diffusion coefficient. No compatibilizer effect was observed in the swelling behavior. [source] Catalytic activities of polymer-supported metal complexes in oxidation of phenol and epoxidation of cyclohexenePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3 2008K. C. Gupta Abstract The metal complexes of N, N,-bis (o -hydroxy acetophenone) propylene diamine (HPPn) Schiff base were supported on cross-linked polystyrene beads. The complexation of iron(III), copper(II), and zinc(II) ions on polymer-anchored HPPn Schiff base was 83.4, 85.7, and 84.5,wt%, respectively, whereas the complexation of these metal ions on unsupported HPPn Schiff base was 82.3, 84.5, and 83.9,wt%. The iron(III) complexes of HPPn Schiff base were octahedral in geometry, whereas copper(II) and zinc(II) ions complexes were square planar and tetrahedral. Complexation of metal ions increased the thermal stability of HPPn Schiff base. Catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in the presence of hydrogen peroxide. The polymer-supported HPPn Schiff base complexes of iron(III) ions showed 73.0,wt% conversion of phenol and 90.6,wt% conversion of cyclohexene at a molar ratio of 1:1:1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 63.8,wt% conversion for phenol and 83.2,wt% conversion for cyclohexene. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 93.1 and 98.3,wt%, respectively with supported HPPn Schiff base complexes of iron(III) ions but was lower with HPPn Schiff base complexes of copper(II) and zinc(II) ions. Activation energy for the epoxidation of cyclohexene and phenol conversion with unsupported HPPn Schiff base complexes of iron(III) ions was 16.6,kJ,mol,1 and 21.2,kJ,mol,1, respectively, but was lower with supported complexes of iron(III) ions. Copyright © 2007 John Wiley & Sons, Ltd. [source] An inference method for temperature step-stress accelerated life testingQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 1 2001Evans Gouno Abstract This paper deals with step-stress accelerated life testing. It presents a practical method to analyse temperature step-stress accelerated life test data. The Arrhenius model is considered. Activation energy and failure rate under operational conditions are estimated both graphically and using maximum likelihood. Applications on simulated data and on real data are presented. Copyright © 2001 John Wiley & Sons, Ltd. [source] Phenol recovery from simulated wastewater using a vertical membrane reactorASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010Manoj Jhanwar Abstract Phenol was recovered from the simulated wastewater in the form of a useful product, allyl phenyl ether, using A-172 membrane as phase-transfer catalyst in a batch and a continuous membrane reactor. The effects of temperature, agitation rates and flow rates of aqueous and organic phases, and concentrations of phenol and allyl bromide on the yield of allyl phenyl ether in the organic phase and phenol removal in the aqueous phase after the reaction were studied. Activation energy and turnover number of the reaction were calculated as well. In the batch mode, the phenol concentration in the treated aqueous phase was found to be < 2 ppm, reduced from 5000 ppm, and more than 99% of the phenol was recovered in the form of allyl phenyl ether after reacting for 180 min. In a continuous mode, the phenol concentration can be reduced from 5000 to 100 ppm in the steady state operation of the reactor. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Chemical Recycling and Kinetics of Aqueous Alkaline Depolymerization of Poly(Butylene Terephthalate) WasteCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2004A.S. Goje Abstract Depolymerization reactions of poly(butylene terephthalate) (PBT) waste in aqueous sodium hydroxide solution were carried out in a batch reactor at 80,140,°C at atmospheric pressure by varying PBT particle size in the range of 50,512.5,,m. Reaction time was also varied from 10,110,min to understand the influence of PBT particle size and reaction time on the batch reactor performance. Agitator speed, particle size of PBT and reaction time required were optimized. Disodium terephthalate (salt) and 1,4-butanediol (BD) remain in the liquid phase. BD was recovered by the salting-out method. Disodium terephthalate was separated by acidification to obtain solid terephthalic acid (TPA). The produced monomeric products (TPA and BD) and PBT were analyzed. The yields of TPA and BD were in agreement with PBT conversion. The depolymerization reaction rate was first order to PBT concentration as well as first order to sodium hydroxide concentration. The acid value of TPA changes with the reaction time as well as particle size of PBT. This indicates that PBT molecules get fragmented and hydrolyze simultaneously with aqueous sodium hydroxide to produce BD and disodium terephthalate. Activation energy, Arrhenius constant, equilibrium constant, Gibbs free energy, enthalpy and entropy were determined. The dependence of the hydrolysis rate constant on reaction temperature was correlated by the Arrhenius plot, which shows an activation energy of 25,kJ/mol and an Arrhenius constant of 438,L/min/cm2. [source] | |||||||||||||||||||||||||||||||||||||||||||